It's got nothing to do with Gmail specifically. I just chose Gmail to illustrate the issue. The same issue / behaviour is exhibited on all apps which have text boxes - messengers, social apps, notes, etc.
The blue pointer cursor won't appear on it's own. You have to tap the text the way you do when you want to move the cursor to a particular point or when you want to select a piece of text.
The cursor shows up upon tapping the text once. From there you can drag it. My point being that it is nearly impossible to drag since 95% of the curson/pointer is hidden behind the keyboard.